The increasing use of pesticides such as herbicides, fungicides, insecticides, etc., poses serious health and environmental problems which must be controlled in order to minimize the harmful effects of those products. One problem frequently encountered with herbicides, such as alachlor, metolachlor, acetochlor, norflurazon and sulfometuron is leaching and migration, which results in loss of herbicidal efficiency and can cause damage to other crops and contaminate water. Alachlor and metolachlor have already been detected in ground water (Yaron et al., 1984, Garner et al., 1986). Thus, only a small fraction of the pesticides applied has desired activity. This imposes repeated applications and increasing cost and ecological damage. It is therefore highly desirable to develop methods which would prevent leaching and migration of pesticides from the top layers of soils, while still maintaining the biological activity in those layers. Ground water contamination by alachlor has been reported in several states of the USA and Canada (Chesters G. et al, 1989; Minnesota Environmental Quality Board, 1988). In most cases alachlor contamination of ground water has been attributed to point source contamination that resulted from improper handling, spills, and leaks (Hung and Frink 1989). However agriculture has been implicated as the non-point source of ground water contamination (Goodrich et al 1991). The downward transport of alachlor to the ground water is controlled primarily by retention and transportation processes. Occurrences of surface and ground water contamination by pesticides including alachlor and metolachlor have been revealed by monitoring programs (Chesters G. et al 1989). Alachlor residues in raw water intakes and tap water is evident (USEPA 1986). Recent monitoring programs show increasing numbers of pesticides in ground water. Cohen et al 1986 reported 17 pesticides in ground water in 23 States of the USA as a result of agricultural practices.
Ground water contamination resulting from the use of alachlor and metolachlor and other herbicides is affected by soil texture, organic matter content, depth to the ground water, temperature, relative humidity, precipitation and irrigation and the amount of herbicide applied. Recent studies on the distribution and dissipation of metolachlor in soil columns (Zheng et al 1993) have shown that the rate of herbicide migration increased with larger doses. Results of this study show that 84-91% of the applied metolachlor was found in the superficial layer (0-9 cm) three days after application, 28 and 56 days after treatment, metolachlor was observed at 21-27 and 27-33 cm depth, respectively. This depth of migration seems more important than described by Bowman (1988, 1989) who reported that metolachlor moved down no more than 10 cm.
As indicated above, the use of available herbicide formulations poses a serious problem of soil and ground water contamination. Such available formulations include soluble concentrate (SC) and emulsion concentrate (EC). Sometimes SC are prepared from chemically modified herbicides whose molecular structure is changed by introducing polar or ionic substituent that increase the solubility in water. This results in an increased leaching in soils. An EC formulation of alachlor has been prepared by the mixing from about 20.0 to about 35.0 percent by weight of alachlor, from about 1.25 to about 1.75 percent by weight of organophylic clay, from about 4.5 to about 9.0 percent by weight of an emulsifier selected from the group consisting of alkyl aryl sulfonates, phosphate esters of nonyl phenol ethoxylates and polyalkyleneglycol ether; from about 10.0 to about 20.0 percentage by weight of an organic solvent in which the herbicide is soluble, which is non reactive to the said herbicide and which is essentially water-soluble, balancing being made up of water (Prill, Erhard J Kirkwood; U.S. Pat. No. 4,440,562).
Another attempt involved a herbicide in fluid suspension consisting of alachlor and chloralkylamino triazine based stabilized product (Arion D; Dorin E; Dragusin E; Katona N; Macaric G; Roibu C; Sarpe N; and Staicu S Rumanian Patent Number RO 137906(890126)). In this attempt the herbicide comprises a 1:1 to 2:1 synergetic ratio alachlor chloralkylamino-s-triazine active substance mix with 20-40% of toluene or xylene as stabilizer and 8-12% mixture of calcium alkyl aryl sulphonate and e.g., polyethoxylated castor oil, 0.5-1.5% of montmorillonitic clay, 1.0-2.5% of ethylene glycol, 0.2-2% of magnesium oxide, blacidic potassium phosphate and borax, remainder water up to 100%. The above mentioned patent was an attempt to improve the herbicidal activity of the herbicide, but ignored the importance of preventing leaching and protecting the groundwater from the contamination by herbicides.
Modification of pesticide behavior by encapsulating the chemicals in a starch matrix is one experimental approach receiving, increased attention (Wing et al 1987). Starch encapsulation has been shown to reduce volatilization (Schreiber et al 1987) and leaching (Gish et al 1991) losses of some herbicides, in this attempt it was found that water potential, imposed using polyethylene glycol, significantly influenced the swelling of the starch matrix and rate of release of both alachlor and atrazine. At 0 MPa water potential complete release requires 21 days for atrazine and 7 days for alachlor. As water potential declined, so did the rate of release (Wienhood and Gish 1992). Results of this work showed that water potential exerts a significant effect on the rate of herbicidal release. It is clear that the ground water is not protected by the use of these encapsulations because the herbicide will be released from the microcapsules and it will leach for certain amounts of water applied. Therefore, this encapsulation approach in a pesticide formulation is not effective in preventing leaching and protecting ground water and soil from herbicide contamination.
Recently, the use of an organo ammonium substituted smectite clay was suggested for controlled release. (Knudson, Jr, Milburn I Gonzales, U.S. Pat. No. 4,849,006). In this attempt controlled release composition is prepared by contacting an organoclay with a biologically active material in concentrated form to cause absorption of the active material in the organoclay. This patent deals with slow release of volatile herbicides to the open atmosphere and does not mention the problem of leaching in soil. In this patent the organoclay is a C12-C18 dialkyl dimethyl ammonium organoclay, or a benzyl ammonium organoclay or a hydroxyalkyl ammonium organoclay. Other organoclays suggested include montmorillonite modified by ammonium cation containing the following four groups: a) C4-C24 alkyl, b) hydrogen, c) benzyl or C4-C24 alkyl, d) hydrogen or C1-C4 alkyl.
It was found that the compounds of this patent do not give satisfactory results.